Anomalous anti-damping in sputtered β-Ta/Py bilayer system

Area of Science:

• Spintronics
• Materials Science
• Condensed Matter Physics

Background:

• Effective damping parameter (αeff) in magnetic thin films is crucial for spintronic device performance.
• Controlling magnetic damping is essential for developing low-power spintronic applications.
• Sputtered Ni81Fe19 (Py) thin films are widely studied for their magnetic properties.

Purpose of the Study:

• To investigate the anomalous decrease in the effective damping parameter (αeff) in Py thin films.
• To explore the influence of a β-Ta layer on the damping properties of Py thin films.
• To understand the underlying physical mechanisms responsible for the observed anti-damping effect.

Main Methods:

• Fabrication of Ni81Fe19 (Py) thin films on SiO2/Si substrates with varying thicknesses of β-Ta layers.
• Measurement of the effective damping parameter (αeff) using techniques sensitive to magnetic damping.
• Analysis of the relationship between β-Ta layer thickness and αeff.

Main Results:

• An anomalous decrease in αeff (anti-damping effect) was observed in Py films with a β-Ta layer, without DC current.
• The reduction in αeff was critically dependent on the β-Ta layer thickness, with the lowest value at 6 nm of β-Ta.
• Interfacial Rashba effect and spin pumping induced spin accumulation in β-Ta were identified as mechanisms, leading to reduced αeff and revealing negative interfacial spin mixing conductance and spin diffusion length.

Conclusions:

• The study demonstrates a novel anti-damping effect in β-Ta/Py heterostructures, tunable via β-Ta layer thickness.
• The findings are attributed to interfacial Rashba effects and spin accumulation-induced spin-orbit torque (SOT).
• β-Ta based nanostructures show promise for developing energy-efficient spintronic devices with tunable damping.